Billy has been with the Call of Aliester since the beginning. And was in fact a boy when the gang formed. He ran with the gang without being formally accepted as a member at the start and usually ran errands for the members. When his friend and mentor Isaiah was killed during a fight with the Delaque. Billy went on a one-boy hunt until he tracked down, isolated and killed each member of the gang responsible for killing Isaiah.
A much older Billy the Boy (the name stuck) still wields his flail and stub gun when heading to a fight. He is absolutely loyal to the Cawdor, the Redemption and to Lucius. In fact he almost always fights at Lucius’ right side. There’s an unspoken bond between them, Billy always knows when some attack is aimed at Lucius’ blindside and Billy always intervenes, protecting Lucius.
Billy’s ability to move through the hive and gather information is very valuable to the Call of Aleister. The skills he used hunting down the Delaque, gathering, analyzing information and using it to manipulate events have turned him into a master of intrigue. He likes his ‘silly’ name of Billy the Boy because it’s hard to take anyone called ‘Billy the Boy’ as a serious threat.